M31_REEC8237_09_SE_CH31.QXD
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All these mushrooms are just the aboveground portion of a
single enormous fungus. Its subterranean network of filaments spreads through 965 hectares of the forest—more than
the area of 1,800 football fields. Based on its current growth
rate, scientists estimate that this fungus, which weighs hundreds of tons, has been growing for more than 1,900 years.
The inconspicuous honey mushrooms on the forest floor
are a fitting symbol of the neglected grandeur of the kingdom Fungi. Most of us are barely aware of these eukaryotes
beyond the mushrooms we eat or the occasional brush with
athlete’s foot. Yet fungi are a huge and important component
of the biosphere. While about 100,000 species have been described, it is estimated that there are actually as many as 1.5
million species of fungi. Some fungi are exclusively singlecelled, though most have complex multicellular bodies,
which in many cases include the structures we know as
mushrooms. These diverse organisms are found in just about
every imaginable terrestrial and aquatic habitat; airborne
spores have even been found 160 km above ground.
Fungi are not only diverse and widespread; they are also
essential for the well-being of most ecosystems. They break
down organic material and recycle nutrients, allowing other
organisms to assimilate essential chemical elements. Humans
make use of fungi as a food source, for applications in agriculture and forestry, and in manufacturing products ranging
from bread to antibiotics. But it is also true that some fungi
cause disease in plants and animals.
In this chapter, we will investigate the structure and evolutionary history of fungi, survey the major groups of fungi,
and discuss their ecological and commercial significance.
Fungi
䉱 Figure 31.1 Can you spot the largest
organism in this forest?
EVOLUTION
CONCEPT
31.1
Fungi are heterotrophs
that feed by absorption
KEY CONCEPTS
31.1 Fungi are heterotrophs that feed by absorption
31.2 Fungi produce spores through sexual or asexual
life cycles
31.3 The ancestor of fungi was an aquatic, single-celled,
flagellated protist
31.4 Fungi have radiated into a diverse set of lineages
31.5 Fungi play key roles in nutrient cycling,
ecological interactions, and human welfare
OVERVIEW
Mighty Mushrooms
Hiking through the Malheur National Forest in eastern Oregon, you might notice a few clusters of honey mushrooms
(Armillaria ostoyae) scattered here and there beneath the towering trees (Figure 31.1). The trees appear to dwarf the mushrooms, but as strange as it sounds, the reverse is actually true.
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UNIT FIVE
The Evolutionary History of Biological Diversity
Despite their vast diversity, all fungi share some key traits, most
importantly the way they derive nutrition. In addition, many
fungi grow by forming multicellular filaments, a body structure
that plays an important role in how they obtain food.
Nutrition and Ecology
Like animals, fungi are heterotrophs: They cannot make their
own food as plants and algae can. But unlike animals, fungi
do not ingest (eat) their food. Instead, a fungus absorbs nutrients from the environment outside of its body. Many fungi
accomplish this task by secreting powerful hydrolytic enzymes into their surroundings. These enzymes break down
complex molecules to smaller organic compounds that the
fungi can absorb into their bodies and use. Other fungi use
enzymes to penetrate the walls of cells, enabling the fungi to
absorb nutrients from the cells. Collectively, the different enzymes found in various fungal species can digest compounds
from a wide range of sources, living or dead.